The present invention relates to a method for synchronizing loads before injection onto a sorting system, in particular a tilt tray type sorting machine. It also relates to a system for the implementation of this method.
These machines are made up of a chain of carts moving around a track, generally in a loop, but which can also be in the form of a rail circuit with semi-autonomous carts using DCV technology, at a predetermined non-zero speed. Each cart is equipped with a tilt tray, which allows for the load being carried to be discharged at a predetermined location, according to known processes.
The invention relates to the injection method, that is, the process allowing for a pre-determined tray to be loaded with a load such as a parcel or a piece of baggage.
Particularly with regard to baggage, the loads have a wide variety of geometrical shapes, materials and various appendages (straps, belts, retractable wheels, etc.) and are of variable masses, which makes their grip, and consequently their kinematic behaviour, practically unpredictable.
The invention describes a method for improving the reliability of injection, that is, the correct positioning of each load taken individually on a sorting machine tray.
The arrows indicate the direction of movement of the loads.
FIG. 1A shows a top view of a set of trays 1AP moving at a pre-determined speed in front of the injection device, which is made up of the following, in the order of movement of the loads:                two spacer type conveyors 1AQ1, 1AQ2 well known in the art, which ensure the movement of the loads one by one towards the actual injection device,        a synchronization conveyor 1AS, the function of which is to place the load in a position allowing for it to be placed on a tray in ballistic mode,        an injection device 1Al, generally made up of a set of drive belts, which carries out such placement.        
The loads are individually presented to the conveyor 1AS according to known processes, which consist of positioning them one by one so that their front edge obscures the photoelectric cells 1AQ1C, 1AQ2C.
As soon as the conveyor 1AS is emptied of the previous load, the conveyor is started according to a pre-determined acceleration law γ1 until the cell 1AS1 is obscured, and then according to a pre-determined acceleration law γ2 until the cell 1AS2 is obscured.
At this stage, the controls simultaneously start the conveyor 1AS and the injection device 1Al to give the load a speed, the component in the direction of travel of the trays on the sorting machine of which is equal to the linear speed of the said trays.
As a point of information, injection at 45° relative to the sorting machine means that this injection speed is of the order of √2× the linear speed of the sorting machine. The means of stabilizing the load despite the transverse component are known. This only occurs when the motorized conveyors are driving the load without any notable sliding or rolling, as shown in FIG. 1B.
When the load does not have the required grip or is likely to roll on the conveyors, the situation is as shown in FIG. 1C, where the load has overshot the obscuring position for the cell 1AS2.
In the known state of the art, this situation, which means that the correct placing of the load on a tray on the sorting machine cannot be foreseen, can be detected.
In the known state of the art, the automatic controls trigger an alarm (for example a stop and a light signal) to request human intervention.
There are injection lines in the known state of the art known as dynamic injection lines, designed in such a way that they only stop the loads if the sorting machine does not have sufficient empty trays to allow for the load to continue moving.
However, if this is not the case, this type of injection line, which largely reproduces the risk related to the load sliding or rolling as already described, also has a stand-by stop.
The management of such incidents presents a certain number of known disadvantages, particularly when the injection line is part of a baggage handling and sorting system.
One of the requirements of such systems is the systematic inspection of the baggage for the detection of any suspicious contents such as explosives.
Such detection takes place through the insertion of a specialist apparatus and intermediate conveyor means upstream of the injection line for final sorting, as illustrated in the diagram in FIG. 1D.
This apparatus includes:                baggage identification means (1D1), for example the optical reading of a bar code printed on a label when the baggage was checked in,        means of detecting the possible presence of suspicious contents (1D2), such as X-ray apparatus.        
After identification, the intermediate conveyor devices and the injection must use known methods to reliably monitor the position of the baggage, in order to keep track of the identification and status, suspicious or not, of each checked piece of baggage.
For example, it is customary to use a sorting machine to send both risk-free baggage to its final destination (aircraft loading station) and baggage that presents a risk to stations for closer inspection.
The slippage of a piece of baggage on injection therefore creates a situation of uncertainty with regard to the location of one or even several pieces of baggage.
In the known injection techniques, the detection of a slippage requires human intervention that consists of:                either removing the piece of baggage for manual handling,        or repositioning it so that it obscures the cell 1AS2 again, which, as long as the control means permit, allows for the normal process to continue with the loss of monitoring considered to be corrected.        
In any case, the said human intervention results in:                operating costs linked to the availability of sufficient competent operators,        risks linked to human error with regard to security.        
For example, some baggage sorting installations are manned to this end by as many operators as injections, thus considerably adding to operating expenses.
In any case, each injection stoppage results in a loss of throughput that prejudices the operational output of the system.